Welcome to the Community!
Let me try to describe it. By installing studio you are not taking any license at start. License will be used when you will start Studio (it depends what type of licensing you will choose). The license is taken also when you will connect a Robot (installed on server) with your Orchestrator tenant. It will take one license per Robot/User which are active at the moment. So if both users are logged in and both have Robot connected then you need to have two license to run two processes simultaneously.
Regarding the error. It means that your tenant have assigned more licenses (you can check them in the Cloud Dashboard) than you really have. If you are on Enterprise plan I suggest contacting with our Technical Support.